The present invention relates to a multi-cylinder engine mounted on a motorcycle.
The number of the cylinders of an internal combustion engine to be mounted on a motorcycle or the like has lately been increased with a view to increasing the upper limit r.p.m. of the engine, to thereby improve engine output power. However, if the cylinders are arranged in the longitudinal direction of the vehicle body, the wheel base of the vehicle is so prolonged as to invite an increase in body weight.
On the contrary, as shown in FIG. 1 a motorcycle which mounts thereon a series multi-cylinder internal combustion engine c having its cylinders b arranged at a right angle with respect to the longitudinal direction of the body a, as shown in FIGS. 1 to 4, has a shorter wheel base, to attain an advantage in body weight. However, the widthwise size of the engine is increased with the increase in the number of the cylinders so that the banking angle .theta..sub.Ai (wherein the letter i designates the number of the cylinders) of the motorcycle is reduced to lower the turning velocity.
On the other hand, if the internal combustion engine is arranged at an upper portion of the body so as to increase the banking angle .theta..sub.Ai, the center of gravity is shifted upwardly to invite a deterioration in slaloming performance.
Further, some motorcycles having a multi-cylinder engine mounted thereon have a construction wherein respective cylinders are equipped with independent carburetors. In this construction, the mounting directions of the respective cylinders are determined exclusively by physical restrictions, e.g., the body structure and the engine mounting positions.
On the other hand, since the carburetor itself is remarkably sensitive to dynamic pressure, vacuum, temperature and the air flow rate, the characteristics of the engine are highly influenced by these parameters. In a multi-cylinder engine having its respective cylinders equipped with independent carburetors, therefore, the carburetors are desirably arranged identically to one another as much as possible.